Relationship between growth temperature and shedding of lipopolysaccharides by gram-negative bacilli

To explore the possibility that physiologically elevated temperatures might reduce the shedding of lipopolysaccharides (LPS) by gram-negative bacteria, the in vitro rates of growth and LPS release by Escherichia coli 055 and Salmonella typhimurium were compared at 33 degrees C, 37 degrees C and 41 degrees C. Rates of LPS accumulation in liquid culture supernatants were measured by radioimmunoassay for O-antigen. Escherichia coli 055 cells, adapted to 35 degrees C and then grown at different temperatures, showed increased growth and LPS release rates parallel with rising incubation temperatures. The growth of a clinical isolate of Salmonella typhimurium (not a laboratory strain) was suppressed slightly at 33 degrees C, but LPS shedding was unaffected by temperature changes. Adaptation of Escherichia coli 055 to 40 degrees C was associated with a smooth-rough transition and a reduced release rate of O-antigen, but no difference in growth rate when compared with a 35 degrees C-adapted strain. Thus, the release rate of LPS by gram-negative bacteria does not necessarily parallel their growth rate. This mechanism does not seem to explain the apparently beneficial effect of fever on the outcome of gram-negative infections in higher animals.